1. Field of the Invention
The present invention relates to a waterproof optical cable having a water containment function to prevent water from spreading in the cable when water enters the cable due to the damage to the sheath of the cable. The present invention also relates to a method of manufacturing the waterproof optical cable.
2. Background of the Invention
A conventional optical cable is provided with a water containment function by continuously or intermittently filling the cable with a waterproofing compound (jelly) such as a petrolatum-group jelly, an oily compound jelly and a polybutene group jelly or with a water-swelling material such as a water-absorbing string, jute, powder and tape. However, as for a spacer-type optical cable having optical fibers or flat optical conductors in the spiral grooves of the peripheral surface of a rodlike spacer, the gap in each of the grooves is so narrow that it is difficult to fill the water-swelling material into the groove. For that reason, the liquid waterproofing compound is generally filled into the groove. Since the gap is made very small in order to prevent the irregularity of the disposition of the optical conductors fitted in the groove and it is extremely difficult to interpose the water-swelling material between the flat optical conductors, the waterproofing compound is fitted in the cable to prevent the spread of water therein, even though the efficiency or ease of manufacturing and connection of the cable is sacrificed. Such an approach is described in the Japanese Patent Application No. 193627/85.
As for the conventional optical cable filled with the water-proofing compound, the temperature and pressure of the compound are made high enough to enhance its flowing property and to perfectly fill the compound in the cable when it is manufactured. At that time, heat and pressure are likely to adversely affect the properties of the optical fiber of the cable. Besides, some difficulty is caused in the manufacturing. Since the compound has a high viscosity and feels unpleasant in the manufacturing of the cable, the efficiency or ease of the work is low. Since the compound clings to the optical fiber, the compound needs to be completely removed from the fiber before the fiber is connected. Therefore, the efficiency or ease of the connection work is very low.
A related U.S. patent application has been filed as Ser. No. 708,769, filed on Mar. 5, 1985, now U.S. Pat. No. 4,703,998, issued 11/3/87.